The precautions are needed, as Gustav is likely to challenge New Orleans' up-armored but unfinished levees. The event is also a test of a complex evacuation plan put into full force Saturday afternoon. Louisiana Lt. Gov. Mitch Landrieu worried Sunday that as many as 20,000 vulnerable New Orleanians had yet to heed the evacuation orders.

"Are the preparations better today than they were before Katrina? Absolutely, positively," says Brian Wolshon, a Louisiana State University emergency response expert. "They took their lumps with Katrina. The problem is there's no telling if conditions will be the same [with Gustav]."

DHS chief Michael Chertoff and FEMA head David Paulson toured the area late in the week as a show of federal support. Mr. Paulson said the preparations indicated "a new philosophy" for the federal government to move aggressively to protect major cities from storms.

The real shift, however, didn't come from FEMA but from DHS, says Cutter. "They already know how to do this stuff," she says of FEMA. But DHS seemed woefully out of touch after Katrina's stormwaters busted through the London, 17th Street, and Industrial canal levees and flooded nearly 80 percent of the Crescent City nearly three years to the day of Gustav's projected landfall.

Gustav was gaining strength Sunday, with tropical force winds extending 200 miles from the eye. But its path is not yet clear; the storm appeared to make a slight jag to the west Sunday morning, amid projections it would make landfall at southwestern Louisiana and then track into Texas as a tropical storm. The greatest threat, authorities say, is the potential for a 20-foot storm surge that could overtop the region's vast fortifications.

As the US Army Corps of Engineers and local authorities rushed to shore up levees on the vulnerable West Bank of New Orleans, which largely escaped Katrina's punch, officials made no promises that up-armored levees would hold. Of particular concern is the Harvey Canal in Jefferson Parish, widely seen as a weak point in the system. In fact, only about one-third of the city's $12 billion new levee system has been completed. With storm-surge projections of up to 20 feet and many levees at eight feet, overtopping seems likely if the storm holds its course.

On Saturday, buses began taking evacuees from 17 points around the city to Union Terminal, where charter buses and trains zipped them out of town. Some 14,000 residents had been moved by the time the bus evacuation ended at noon Sunday. The Super Dome, the scene of such misery after Katrina, will be locked and guarded. There will be no "shelter of last resort," authorities say. If there were any doubts about the storm's potential, Mayor Nagin extinguished those Saturday night when he used unusually strong language to urge people to leave, calling Gustav "the storm of the century" and "the mother of all storms."

"You need to get your butts out," the famously laid-back mayor told residents Saturday night, taking a much sharper tone than during the pre-Katrina days. "You need to be scared."

New Orleanians took notice. Resident Patrick Green said the city, which has regained nearly 90 percent of its residents since Katrina, had finally begun to feel normal. "I don't know where I'm going, but it doesn't matter: It's time to go," says Mr. Green. Looking around at the mostly empty streets, Green says, "I'm leaving a ghost town."

Yet hopes for a 100 percent evacuation dimmed Sunday morning as authorities declared a noon deadline to hop an evacuation bus. What had been a crush of evacuees had slowed through Saturday. "I'm a little troubled," says Lieutenant Governor Landrieu.

The evacuation was not eventless. Traffic on Saturday was backed up more than 20 miles on I-10 into Mobile, Ala. A new ID bracelet system intended to link evacuees together via the Web crashed on Saturday at Union Terminal. Officials said evacuees will instead be logged in at shelters, but those added logistics may become daunting in the next few days because shelters are spread across the Gulf Coast and may not be equipped to log in evacuees. One logistics contractor, David Young, said the city seemed to be scrambling on some fronts to prepare. In Jefferson Parish, some 700 people waited in vain Saturday for buses to pick them up, according to reports.

Garden District resident Alan Drake, a gardener, says he plans to stay, as he did through Katrina. "I'll have a lot of my clients' homes cleaned up by the time they get back," he says.

"We've got quite a few people staying, most of them from Mexico and Puerto Rico," says New Orleans resident Fred Wilson, who stayed through Katrina before being evacuated two weeks later at gunpoint. "I think people are saying they'll survive the best they can. But this is a greater force than Katrina."

After Katrina, the city partnered with emergency experts and charities to figure out how to appeal to the most vulnerable residents, the elderly, to leave during storm emergencies, says John Kiefer, an emergency expert at the University of New Orleans. Yet the city began distributing pamphlets explaining the new procedures only last week.

Mr. Kiefer says officials were surprised to learn that the elderly hung on through Katrina because of the uncertainties implicit in an emergency evacuation. To assuage that, officials have been clearer about where evacuees are going and where they'll be staying. Residents who returned, too, "have a different risk perspective," says Cutter of the University of South Carolina. "The people who came back are really committed to the city, and this is all very personal to them now."

Abandoned pets became a huge issue during Katrina, triggering special legislation in Lousiana to avoid the misery of survival for animals in a flooded city. Animal rescue groups scrambled over the weekend to take possession of pets at Union Terminal Station, to be returned after the storm. Unlike during Katrina, many residents were allowed to take small, and sometimes larger, animals on the evacuation buses.

"I'm still praying this is just a big drill," says animal rescue worker Brenda Shoss, wearing a duct-tape name tag.

Those who stay will encounter a skeleton crew of law-enforcement officers who will treat anybody on the street as a suspicious person, says Aaron Broussard, president of Jefferson Parish. The idea is to guarantee that property will be protected against looters – a main reason so many residents decided to ride out Katrina. "If you stay," Mr. Broussard warns, "this will be no Mayberry."

"We've learned from our mistakes," says New Orleans Police Officer B. Francois. "And this time, if we arrest someone, they're not going to the local jail. They're getting on a bus to Angola," the infamous rural prison farm.

Outside New Orleans, many shrimpers, who lost most of their fleet to Katrina, skippered boats up into inland waters. Others secured them as well as they could to the docks in eastern Orleans Parish.